Wire frame structures for spectacles have been in existence for a long time. Spectacle lenses are fastened to such wire frame structures by bolting systems or the like, the lenses then not being surrounded by the frame, i.e. being rimless. Each spectacle lens is then provided with one or more through holes and/or a through notch in the nose zone and in the temple zone of said lens. In order to secure each lens pierced in this way to a wire frame portion having a hinged arm, various mechanical fastening means have been proposed, the most common of which is constituted by bolting.
The problem then arises of how to perform the various machining in the nose zones and in the temple zones of the spectacle lenses as simply and as precisely as possible.
Document JP-A-8 155 945 describes a lens-drilling unit making it possible to form two through holes in the vicinities of respective ones of two opposite edges of each lens. That document describes a machining assembly having a structure that is very complex and expensive. Document JP-A-8 155 806 also describes a drill assembly having oscillating lens supports. For the purpose of drilling particular holes in lenses, reference can also be made to Document WO-A-00/68 729 describing a drill assembly serving to form oblong through holes, and to Document WO-A-99/37 449 describing a drill assembly adapted to machining blind holes in the thickness of the lens.
Unfortunately, the drill assemblies described in the above-mentioned documents are of complex structure and of high-cost.
Reference can also be made to Document FR-A-2 800 172 describing a method of drilling holes in lenses that is computer-aided so as to associate drilling plans with a given virtual lens template.
Document EP-A-0 739 683 describes an assembly for drilling holes in spectacles. That assembly is designed to form holes and notches in lenses. It provides a two-dimensional X,Y slide positionable on an angularly positionable guide mounted on a bed. While the lenses are being machined, the lens supports are moved relative to the drill tool in a horizontal plane, without rotation.
Document WO 00/67 974 describes apparatus for drilling holes in lenses with a complete system for supporting two drills. Each support is mounted to slide in horizontal translation, thereby making it possible to form a hole and a notch or two holes by two successive machining operations along a rectilinear path.
In general, if a numerically-controlled drill is used, the points to be machined are always identified on the basis of indexing from the center of the lens, said center being considered to be a reference zero point forming the origin of two coordinate axes in a horizontal plane. When the vertical axis of the drill tool is brought vertically over the center of the lens, the machine is calibrated, so that any subsequent X,Y movement makes it possible to position the tool exactly for the purpose of drilling the lens at a given point thereof. However, in order to perform such drilling, it is necessary for the numerically-controlled drill to store in a memory all of the shapes of lenses that are to be used, because each lens must be provided with holes and/or notches in the vicinities of its nose zone and of its temple zone at precise distances from the free edges of the lens. As a result, that technique is, de facto, limited to very conventional lens shapes, in particular circular, oval, square, or rectangular shapes, of outline pre-stored in a memory. The operator must then, on each occasion, search the memory for the corresponding lens outline, and then also search the memory for the desired machining pattern for the chosen lens. Such search requirements represent major constraints for operators, not to mention the risks of errors in the event that an outline is incorrectly stored in the memory. As a result, numerically-controlled drills used for drilling holes in lenses remain expensive and voluminous machines, which are reserved for large assembly workshops.
A need therefore exists for a mechanical drill that is more compact and easier to handle, and that opticians can use in their stores or in their assembly workshops.
Recently, a numerically-controlled mechanical drill has been proposed that was specially developed to form through notches in lenses, and optionally also holes. To this end, reference can be made to Document FR-A-2 826 599. That document describes a drill whose drill tool is movable manually in a vertical direction. In the associated method of implementation, provision is made to position the lens in a plane that is essentially perpendicular to the axis of rotation of the drill tool, so that the corresponding edge of the lens finds itself in abutment against the drill tool, which is then stationary, at a point of contact that is pre-marked on the lens, and the lens is held stationary in that position. It is only then that the drill tool is caused to rotate, and the lens is turned (moved in rotation) relative to the drill tool in a horizontal plane about a fixed point distinct from the axis of the drill tool, the amplitude of the turning movement corresponding to the length of the through notch that is to be machined. Then, the drill tool is moved away from the lens by manually raising said tool along its axis.
Such a mechanical drill constitutes an advantageous tool, but the approach used cannot be transposed to numerically-controlled drills.